Thrombin is an important serine protease in hemostasis and thrombosis. One of the key actions of thrombin is cellular modulation via receptor activation. A functional human thrombin receptor (PAR-1), cloned by Coughlin in 1991 (T.-K. Vu, Cell 1991, 64, 1057), was found to be a member of the G-protein coupled receptor (GPCR) superfamily. The receptor activation putatively occurs by N-terminal recognition and proteolytic cleavage at the Arg-41/Ser42 peptide bond to reveal a truncated N-terminus. This new receptor sequence, which has an SFLLRN (Ser-Phe-Leu-Leu-Arg-Asn) N-terminus acting as a tethered ligand to recognize a site on the receptor, can trigger activation and signal transduction leading to platelet aggregation. Since 1991, three other protease-activated receptors with extensive homology to the thrombin receptor, “PAR-2” (S. Nystedt, Proc. Natl. Acad. Sci USA 1994, 91, 9208), “PAR-3” (H. Ishihara, Nature 1997, 386, 502), and “PAR-4” (W.-F. Xu, Proc. Natl. Acad. Sci USA 1998, 95, 6642), have been cloned. Thrombin receptor (PAR-1) specific antibody-induced blockade of the platelet thrombin receptor has shown efficacy against arterial thrombosis in vivo (J. J. Cook Circulation 1995, 91, 2961). Hence, antagonists of the thrombin receptor (PAR-1) are useful to block these protease-activated receptors and, as such, may be used to treat platelet mediated thrombotic disorders such as myocardial infarction, stroke, restenosis, angina, atherosclerosis, and ischemic conditions.
The thrombin receptor (PAR-1) has also been identified on other cell types: endothelial, fibroblast, renal, osteosarcoma, smooth muscle, myocytes, tumor, and neuronal/glia. Thrombin activation of endothelial cells upregulates P-selectin to induce polymorphonuclear leukocyte adhesion—an inflammatory response of the vessel wall (Y. Sugama, J. Cell Biol. 1992, 119, 935). In fibroblasts, thrombin receptor (PAR-1) activation induces proliferation and transmission of mitogenic signals (D. T. Hung, J. Cell Biol. 1992, 116, 827). Thrombin has been implicated in osteoblast proliferation through its activation of osteoblast cells (D. N. Tatakis, Biochem. Biophys. Res. Commun. 1991, 174, 181). Thrombin has been implicated in the regulation and retraction of neurons (K. Jalink, J. Cell. Biol. 1992, 118, 411). Therefore, in this context, the antagonist compounds of this invention may also be useful against inflammation, osteoporosis, Angiogenesis related disorders, cancer, neurodegenerative disorders, hypertension, heart failure, arrhythmia, glomerulonephritis.
The compounds of the present invention are a structurally novel class of indazole peptidomimetics represented by the general formula (I) below.